1 files changed, 257 insertions, 0 deletions
diff --git a/src/newgidmap.c b/src/newgidmap.c
new file mode 100644
index 0000000..7fcb459
--- /dev/null
+++ b/src/newgidmap.c
@@ -0,0 +1,257 @@
+/*
+ * Copyright (c) 2013 Eric Biederman
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the copyright holders or contributors may not be used to
+ *    endorse or promote products derived from this software without
+ *    specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ * PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT
+ * HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include "defines.h"
+#include "prototypes.h"
+#include "subordinateio.h"
+#include "idmapping.h"
+
+/*
+ * Global variables
+ */
+const char *Prog;
+
+
+static bool verify_range(struct passwd *pw, struct map_range *range, bool *allow_setgroups)
+{
+	/* An empty range is invalid */
+	if (range->count == 0)
+		return false;
+
+	/* Test /etc/subgid. If the mapping is valid then we allow setgroups. */
+	if (have_sub_gids(pw->pw_name, range->lower, range->count)) {
+		*allow_setgroups = true;
+		return true;
+	}
+
+	/* Allow a process to map its own gid. */
+	if ((range->count == 1) && (pw->pw_gid == range->lower)) {
+		/* noop -- if setgroups is enabled already we won't disable it. */
+		return true;
+	}
+
+	return false;
+}
+
+static void verify_ranges(struct passwd *pw, int ranges,
+	struct map_range *mappings, bool *allow_setgroups)
+{
+	struct map_range *mapping;
+	int idx;
+
+	mapping = mappings;
+	for (idx = 0; idx < ranges; idx++, mapping++) {
+		if (!verify_range(pw, mapping, allow_setgroups)) {
+			fprintf(stderr, _( "%s: gid range [%lu-%lu) -> [%lu-%lu) not allowed\n"),
+				Prog,
+				mapping->upper,
+				mapping->upper + mapping->count,
+				mapping->lower,
+				mapping->lower + mapping->count);
+			exit(EXIT_FAILURE);
+		}
+	}
+}
+
+static void usage(void)
+{
+	fprintf(stderr, _("usage: %s <pid> <gid> <lowergid> <count> [ <gid> <lowergid> <count> ] ... \n"), Prog);
+	exit(EXIT_FAILURE);
+}
+
+void write_setgroups(int proc_dir_fd, bool allow_setgroups)
+{
+	int setgroups_fd;
+	char *policy, policy_buffer[4096];
+
+	/*
+	 * Default is "deny", and any "allow" will out-rank a "deny". We don't
+	 * forcefully write an "allow" here because the process we are writing
+	 * mappings for may have already set themselves to "deny" (and "allow"
+	 * is the default anyway). So allow_setgroups == true is a noop.
+	 */
+	policy = "deny\n";
+	if (allow_setgroups)
+		return;
+
+	setgroups_fd = openat(proc_dir_fd, "setgroups", O_RDWR|O_CLOEXEC);
+	if (setgroups_fd < 0) {
+		/*
+		 * If it's an ENOENT then we are on too old a kernel for the setgroups
+		 * code to exist. Emit a warning and bail on this.
+		 */
+		if (ENOENT == errno) {
+			fprintf(stderr, _("%s: kernel doesn't support setgroups restrictions\n"), Prog);
+			goto out;
+		}
+		fprintf(stderr, _("%s: couldn't open process setgroups: %s\n"),
+			Prog,
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	/*
+	 * Check whether the policy is already what we want. /proc/self/setgroups
+	 * is write-once, so attempting to write after it's already written to will
+	 * fail.
+	 */
+	if (read(setgroups_fd, policy_buffer, sizeof(policy_buffer)) < 0) {
+		fprintf(stderr, _("%s: failed to read setgroups: %s\n"),
+			Prog,
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+	if (!strncmp(policy_buffer, policy, strlen(policy)))
+		goto out;
+
+	/* Write the policy. */
+	if (lseek(setgroups_fd, 0, SEEK_SET) < 0) {
+		fprintf(stderr, _("%s: failed to seek setgroups: %s\n"),
+			Prog,
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+	if (dprintf(setgroups_fd, "%s", policy) < 0) {
+		fprintf(stderr, _("%s: failed to setgroups %s policy: %s\n"),
+			Prog,
+			policy,
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+out:
+	close(setgroups_fd);
+}
+
+/*
+ * newgidmap - Set the gid_map for the specified process
+ */
+int main(int argc, char **argv)
+{
+	char proc_dir_name[32];
+	char *target_str;
+	pid_t target;
+	int proc_dir_fd;
+	int ranges;
+	struct map_range *mappings;
+	struct stat st;
+	struct passwd *pw;
+	int written;
+	bool allow_setgroups = false;
+
+	Prog = Basename (argv[0]);
+
+	/*
+	 * The valid syntax are
+	 * newgidmap target_pid
+	 */
+	if (argc < 2)
+		usage();
+
+	/* Find the process that needs its user namespace
+	 * gid mapping set.
+	 */
+	target_str = argv[1];
+	if (!get_pid(target_str, &target))
+		usage();
+
+	/* max string length is 6 + 10 + 1 + 1 = 18, allocate 32 bytes */
+	written = snprintf(proc_dir_name, sizeof(proc_dir_name), "/proc/%u/",
+		target);
+	if ((written <= 0) || (written >= sizeof(proc_dir_name))) {
+		fprintf(stderr, "%s: snprintf of proc path failed: %s\n",
+			Prog, strerror(errno));
+	}
+
+	proc_dir_fd = open(proc_dir_name, O_DIRECTORY);
+	if (proc_dir_fd < 0) {
+		fprintf(stderr, _("%s: Could not open proc directory for target %u\n"),
+			Prog, target);
+		return EXIT_FAILURE;
+	}
+
+	/* Who am i? */
+	pw = get_my_pwent ();
+	if (NULL == pw) {
+		fprintf (stderr,
+			_("%s: Cannot determine your user name.\n"),
+			Prog);
+		SYSLOG ((LOG_WARN, "Cannot determine the user name of the caller (UID %lu)",
+				(unsigned long) getuid ()));
+		return EXIT_FAILURE;
+	}
+
+	/* Get the effective uid and effective gid of the target process */
+	if (fstat(proc_dir_fd, &st) < 0) {
+		fprintf(stderr, _("%s: Could not stat directory for target %u\n"),
+			Prog, target);
+		return EXIT_FAILURE;
+	}
+
+	/* Verify real user and real group matches the password entry
+	 * and the effective user and group of the program whose
+	 * mappings we have been asked to set.
+	 */
+	if ((getuid() != pw->pw_uid) ||
+	    (getgid() != pw->pw_gid) ||
+	    (pw->pw_uid != st.st_uid) ||
+	    (pw->pw_gid != st.st_gid)) {
+		fprintf(stderr, _( "%s: Target %u is owned by a different user: uid:%lu pw_uid:%lu st_uid:%lu, gid:%lu pw_gid:%lu st_gid:%lu\n" ),
+			Prog, target,
+			(unsigned long int)getuid(), (unsigned long int)pw->pw_uid, (unsigned long int)st.st_uid,
+			(unsigned long int)getgid(), (unsigned long int)pw->pw_gid, (unsigned long int)st.st_gid);
+		return EXIT_FAILURE;
+	}
+
+	if (!sub_gid_open(O_RDONLY)) {
+		return EXIT_FAILURE;
+	}
+
+	ranges = ((argc - 2) + 2) / 3;
+	mappings = get_map_ranges(ranges, argc - 2, argv + 2);
+	if (!mappings)
+		usage();
+
+	verify_ranges(pw, ranges, mappings, &allow_setgroups);
+
+	write_setgroups(proc_dir_fd, allow_setgroups);
+	write_mapping(proc_dir_fd, ranges, mappings, "gid_map", pw->pw_uid);
+	sub_gid_close();
+
+	return EXIT_SUCCESS;
+}